1990 Chevy truck dies at random


#1

My truck is having a problem lately where it will suddenly die while driving. It feels like it loses either spark or fuel and happens about 20-30 minutes after I drive it. Once it dies you can turn the key off and restart it and it will fire up and run again, for how long I’m not sure because I’m almost home about that time. It has a fairly new fuel pump, 2 years old, a fuel filter the same age, new cap and rotor, new air filter, probably could use some new plugs. I replaced the TPS with an older one that I had laying around and had no change in performance. I get a 34 and 43 code (MAP and knock sensor) when I do a diagnostic on it.
My question is do you think a MAP sensor or knock sensor would cause this kind of failure before I go out and buy them? I’m leaning towards the MAP sensor but not sure that it would have this kind of an effect on the engine.
Thanks for your help!


#2

Those codes don’t say that either your MAP or knock sensors are bad. They basically refer to electrical signals. (34 is a low voltage signal from the MAP; 43 is a knock sensor circuit fault).

So here’s an alternative scenario. You have a spot on a wiring harness that is damaged. Its creating both of those codes along with whatever else is causing the engine to shut down. Take a close look at that. Follow the wires away from the sensors if you need to.


#3

Thanks, I’ll try to find a scuffed wire and see if that may be the cause. By the way, I checked the electrical connections (weatherpack terminals) on all the sensors on top of the engine, including the distributor, and all looked to be clean inside and wires intact.


#4

I think the standard answer would be the crank sensor. I spent months trying to find the same problem on my Buick and finally just junked it after a crank sensor, ignition switch, computer, etc. Ran around each night with a fuel pressure tester taped to the windshield and a test light trying to see what was failing. Neither I nor the mechanics could solve it sorry to say. I don’t think those codes are pointing to the problem.


#5

Well, checked all the wires under the hood and all seem fine. I even crawled under the truck and looked at any wires I could find there; good as well. As far as a crank sensor problem, this engine doesn’t have one. This engine has a distributor with a magnetic pickup and a single coil, which I’m not rulling out the pickup as a suspect as it is original (190,000 miles) to the truck. I should have said earlier that this is a 350 V8 w/manual trans. 2WD. I drove the truck today with no problems. Made my whole trip to work and home again just fine. I tried a test just to see what would happen and unplugged the MAP sensor while the truck was running and it died right away. There is a test you can do on a MAP sensor but it requires a digital volt meter of which I don’t have, It may be time to buy one. I think I’ll drive it for a while and see if it happens again and if it does I’ll do a test on the MAP sensor.